UIView extension to quickly add and fit or center a subview inside a superview, using constraints

MyView.swift

class MyView : UIView {
 
  func buildMyView() {
    var indicatorView :UIActivityIndicatorView!
    let indicatorSize : CGFloat = 120
    loadingIndicator = UIView(frame: CGRect(origin: CGPoint.zero, size: CGSize(width: indicatorSize, height: indicatorSize)))
    loadingIndicator.backgroundColor = UIColor.darkGray.withAlphaComponent(0.7)
    loadingIndicator.layer.cornerRadius = 10.0
    indicatorView = UIActivityIndicatorView(activityIndicatorStyle: .white)
    indicatorView.hidesWhenStopped = false
    
    let inset :CGFloat = 20.0
    let insets = UIEdgeInsets(top: inset, left: inset, bottom: inset, right: inset)
    loadingIndicator.fit(subView: indicatorView, .horizontallyAndVertically, with: insets)
    view.center(subView: loadingIndicator, orientated: .horizontallyAndVertically, withOffsets: CGPoint(x: 0, y: -100))
  }
  
}

ViewExtensions.swift

//
//  ViewExtensions.swift
//
//  Created by Dermot O Sullivan on 31/1/17.
//

import Foundation

enum FitOrientation {
    case horizontally
    case vertically
    case horizontallyAndVertically
}

extension UIView {
    
    /** Center the provided view in current view by adding necessary constraints, and adding the view as a subview, if needed.
     - parameter view: The subview to be added. Must have intrinsic size or height and width manually set.
     
     */
    func center(subView view:UIView, orientated orientation:FitOrientation = .horizontallyAndVertically) {
        center(subView: view, orientated: orientation, withOffsets: CGPoint.zero)

    }
    /** Center the provided view in current view by adding necessary constraints, and adding the view as a subview, if needed.
     - parameter view: The subview to be added. Must have intrinsic size or height and width manually set.
     - parameter offset: The offset from the center to use.
     
     */
    func center(subView view:UIView, orientated orientation:FitOrientation = .horizontallyAndVertically, withOffsets offset:CGPoint) {
        if view.superview != self {
            self.addSubview(view)
        }
        view.translatesAutoresizingMaskIntoConstraints = false
        if orientation == .horizontally || orientation == .horizontallyAndVertically {
            let constraint = NSLayoutConstraint(item: view, attribute: .centerX, relatedBy: .equal, toItem: view.superview!, attribute: .centerX, multiplier: 1.0, constant: offset.x)
            addConstraint(constraint)
        }
        
        if orientation == .vertically || orientation == .horizontallyAndVertically {
            let constraint = NSLayoutConstraint(item: view, attribute: .centerY, relatedBy: .equal, toItem: view.superview!, attribute: .centerY, multiplier: 1.0, constant: offset.y)
            addConstraint(constraint)
        }
    }

    
    /** Fit the provided view in current view by adding necessary constraints, and adding the view as a subview, if needed */
    func fit(subView view:UIView, _ orientation:FitOrientation = .horizontallyAndVertically, with padding:UIEdgeInsets = UIEdgeInsets.zero) {
        if view.superview != self {
            self.addSubview(view)
        }
        view.translatesAutoresizingMaskIntoConstraints = false
        
        if orientation == .horizontally || orientation == .horizontallyAndVertically {
             self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-\(padding.left)-[subview]-\(padding.right)-|", options: .directionLeadingToTrailing, metrics: nil, views: ["subview": view]))
        }
        
        if orientation == .vertically || orientation == .horizontallyAndVertically {
             self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|-\(padding.top)-[subview]-\(padding.bottom)-|", options: .directionLeadingToTrailing, metrics: nil, views: ["subview": view]))
        }
    }
}